As suggested by many experts and GMAT takers, MGMAT SC
Guide is a good guide which covers all the topics in a very systematic manner. It is especially great if you are not very good with basic English Grammar, in which case you should start with their Foundation to GMAT Verbal book.
Note: I might be a little biased, given the fact that I have studied from MGMAT SC
. Also, at the end of the day all depends on the amount of hard work and practice you do.
All the best
Press Kudos if the post helped